1. Field of the Invention
This invention relates to tools for attaching connectors to coaxial cables. More specifically, this invention relates to tools which deform a thin-walled portion of the connector into a uniform circumferential seal around the cable by driving the connector in a direction parallel to the axis of the cable into a conically tapered cavity in a die to produce a radially tapered crimp.
2. Description of Related Art
A common type of electrical connector used on coaxial cables includes a thin-walled cylindrical portion at the end of the connector which receives the cable. The coaxial cable is prepared by removing insulation and exposing the inner conductor and the outer conductive braid. The prepared cable is then inserted into the thin-walled cylindrical portion at the back end of the connector, and the thin-walled portion is radially compressed around the cable with a hand tool.
The compression operation simultaneously connects the outer connector housing to the outer conductive braid, and mechanically connects the connector to the cable. Connectors of this type are widely used in the cable industry for connecting coaxial cables that carry video signals.
A variety of hand tools have been designed to compress the thin-walled cylindrical portion of the connector. Some tools apply the compression force directly inward, transverse to the axis of the cable and radially inward from opposite sides of the connector. However, an alternative design for a compression tool applies the compression force longitudinally, i.e., along the axis of the cable and connector. The axially directed force is applied to the front of the connector which drives the thin-walled portion at the back end of the connector into a conically tapered die. The cone-shape of the die converts the axial or longitudinal force into a radial force and swages the thin-walled portion into a relatively uniform and smoothly tapered compression fit between the connector and the cable.
One problem with this type of design has been the difficulty of extracting the connector from the tapered die after the compression cycle. In prior art tools of the type shown in U.S. Pat. No. 5,392,508, only one half of the tapered die is movable, and the other half of the die is rigidly attached to the tool. In this type of design, the compressed connector can be so deeply forced into the die that it locks the two die halves together, making it difficult to open them. Because only one half of the die is moveable, the moveable half must move longitudinally a short distance relative to the other half before it swings away to open the die. This relative longitudinal/axial motion between the two die halves is resisted by the connector which is in firm contact with both die halves after the compression cycle.
Another problem with prior art tools is the failure of the tool to hold the thin-walled portion of the connector in alignment with, and squarely perpendicular to, the plunger portion of the tool which provides the compression force. When correct alignment is not maintained, the connector will not be compressed properly, and may jam in the tapered cavity. At the same time, it is desirable to keep the hand tool light in weight and inexpensive to manufacture.
Heretofore, compression tools of this type, as exemplified in U.S. Pat. No. 5,392,508, have all used a C-shaped frame. The C-frame has a back portion which must rigidly hold two projecting arms in accurate and parallel alignment during the compression operation. The two arms In a C-frame design define a compression region between them within which the connector is positioned. A plunger projects into the compression region through one arm of the C-frame, and the connector is driven into the conically tapered cavity in the die which is supported by the opposing arm of the C-frame. The back portion of the C-frame is relied upon and must be strong enough to hold the two arms parallel to each other throughout the compression operation.
In order to keep the front of the connector square relative to the die cavity, the back and two arms of the C-frame must be relatively large and strong, making them heavy. It is particularly difficult to keep the back straight and still keep the frame light, because the back portion of a C-frame is under a relatively high bending moment and is partially in compression and partially in tension. If the back and arms of the C-frame are not sufficiently stiff, the frame will distort as the compression forces are applied. Such distortion lets the two arms of the C-frame move away from parallel resulting in an improperly compressed connector that may fail, or which may jam in the die. Making the C-frame stiffer usually requires more weight which adds cost and is undesirable for the user who may have to lift and carry the tool tens of thousands of times during its life.
The present invention addresses the problem of maintaining tool alignment during compression through the use of an O-frame which permits a reduction in weight and materials cost, while improving tool rigidity. By improving tool rigidity, the problem of connector jamming is also reduced. To make the compressed connector easier to remove and for the occasional jammed connector that results in all such designs, the tool is designed with two identical pivoted die halves. By pivoting both die halves the die is much easier to open, even when a misaligned connector has been jammed into the die. By making the die halves identical, tool cost is reduced.
The jamming problem has also been made easier to deal with, and tool operation speed increased, by attaching die handles to the die halves. The die handles point forward and are arranged in close parallel proximity to each other so that they can be quickly squeezed together to open the die and allow the connector to be removed.
A further problem with prior art tool designs has been the "full-cycle" ratchet mechanism. A full-cycle ratchet mechanism forces the tool to progress through a complete compression cycle before the handles of the tool can be opened. This is advantageous for ensuring that a full stroke is applied to the tool handles to fully complete each compression operation, but it creates a problem when the tool operator discovers that a connector is misaligned and is about to jam in the die cavity. Prior art tools, such as the type shown in U.S. Pat. No. 5,743,131, have required a tool, such as a screwdriver, to release the full-cycle ratchet mechanism before the compression cycle is complete. This is inconvenient, and may tempt the operator to try to complete the compression cycle, jamming the connector more deeply and worsening the problem. The present invention addresses this problem with a hand-operable release for the full-cycle ratchet mechanism.
Another problem with prior art tools has been the adjustment mechanism. To ensure a perfectly compressed connector, the distance between the plunger and the tapered die cavity must be carefully controlled. Tool wear causes this distance to change. Prior art tools have provided a single adjustment to the plunger to compensate for such wear, but the adjustment is difficult. The present invention provides two separate adjustments, one coarse adjustment and one fine adjustment that allows the operator to quickly make fine or coarse adjustments to the tool.
Yet another problem with prior art devices relates to the interconnection between the handle providing the compression force and the plunger performing the compression. Typically, as the handles are opened, the plunger is pulled towards the retracted position by a link. Some prior art designs have locked into the open position when the handles open too far and the link passes over center. The present invention addresses this difficulty with an enlarged plunger head which limits rearward motion of the plunger.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a radial taper tool which is light in weight, has low material cost, and is not subject to distortion during the compression operation.
Another object of the present invention to provide a radial taper tool which resists jamming.
Yet another object of the present invention to provide a radial taper tool with a full-cycle ratchet mechanism that is rugged and yet is easy to release prematurely, without tools, when desired.
It is another object of the present invention to provide a radial taper tool which allows the cable and compressed connector to be easily and quickly removed from the tool after the connector is compressed.
A further object of the present invention is to provide a design which can be easily adjusted to high accuracy.